Eta-plane horn



June 10, 1952 Filed Jan. 16, 1946 FIG.I

FIGEB INVENTOR LAN JEN CHU ATfORNEY Patented June 10, 1952 H-PLANE HORNLan Jen Chu, Brookline, Mass., assignor, by mesne assignments, to theUnited States of America as represented by the Secretary of the NavyApplication January 16, 1946, Serial No. 641,606.

1 V This invention relates in general to high frequency directive energytransmission and reception, and more particularly concerns the novelstructure of an electromagnetic horn of improved radiationcharacteristics. 7 I

An electromagnetic horn comprises, broadly, a flared conductive radiatorused for the interchange of wave energy between space and a transmissionline and provides a directive or sharply defined radiation pattern. Thefield pattern obtained by the use of a horn at a particular frequency isa function of the shape and dimensions of the major opening or hornaperture which in turn is determined by the flare angle and horn length.The horn is coupled to a transmission line at the constricted or throatend thereof. 'I'hedirectional properties of the horn are the same fortransmission or reception, and the directivity may be effectivelyincreased by the addition of a reflector.

In various applications a horn radiator introduces undesirable features.As an example consider the representative problem of a low angle, orsurface search radar system which utilizes a horn for the transfer ofenergy between a transmission line and a reflector, which in turnprovides-a radiation pattern with a principal lobe directed toward thehorizon and parallel to the earth. The use of a conventional hornradiator results in an overall radiation pattern which in-- cludesundesirable side lobes, also parallel to the surface of the earth and atright angles to the principal lobe. Although the energy content of theright angle lobes is considerably less than that of the major lobe,these side lobes will pro-- duce on an indicator incorrect and confusingtarget indications. It is therefore a specific object of my invention toprovide an electromagne'tic. horn. radiator having a field patternincluding a principal lobeand side lobes oriented such as to eliminatesubstantially all spurious response. 1

Anotherobjectof my invention is to provide an electromagnetic. hornradiator of asymmetrical structure.

A further object of my invention is to provide a hornradiator which incombination with .a reflector produces an overall radiation patterncomprising a sharp, directional principal beam and minor side beamselevated with respect to the principal beam.

These and other objects of my invention will now become apparent fromthe following detailed specification taken in connection with the.accompanying drawings in which:

7 Claims. (Cl. 250-3315) 1 surface; and

Fig. 3 illustrates the radiation pattern of the horn radiatorillustrated in Fig. 2 in a plane Fig. l is a general perspective view ofthe novel electromagnetic horn of my invention;

Fig. 2 illustrates diagrammatically the combination of the horn of Fig.1 and a reflecting passing through the axis IIIIII of Fig. 2-andnormalto the plane of Fig.2.

Referring now to Fig. 1, there is illustrated an electromagnetic hornembodying the principles of my present invention. This horn structurecomprises essentially a transmission line extension or input end ll ofsubstantially rectangular cross section, adapted for coupling to acorresponding rectangular wave guide transmission system (not shown).The longitudinal axis I2 of the rectangular input section ll comprisesalso the axis of the horn l0 and indicates the direction of en'- ergytransmission therethrough. The horn I0 is a pyramidal conductivestructure extending from a rectangular throat-section l3 at the junctionwith input section II to a comparatively large rectangular aperture M.This flared section is} constructed of four substantially trapezoidalmetallic plates, two of which l5 and I6 are narrow and the other two ofwhich I! and I8 are comparatively broad.

erture I 4 of the horn is fixed in non-perpendicular relationship withthe axis I2 of energy prop-' agation through the horn. The angle betweenthe plane of aperture l4 and the normal to the axis I2 is designated asangle 0 on the drawing.

The angle between the plane of the rectangular throat l3 and the normalto the axis I2 is also made equal to 0, thereby permitting the broadwalls [1 and [8 to be plane trapezoids rather than warped surfaces. 1

The horn illustrated in Fig. 1 may be utilized to interchange energybetween a transmission line and space. For example, if the horn isutilized in a transmitter system, energy coupled thereto I atrectangular input section II will be radiated from the rectangularaperture It. If the horn is utilized in connection with a receiver,energy intercepted by the aperture [4 will be delivered to thetransmission line section coupled at section I I. Energy radiated fromthe horn of Fig. 1 is directional in nature, and the directivity thereofis primarily a function of the flare angle of the born between .thethroat section l3 and the aperture M. For the pyramidal horn, asillustrated in Fig.

.' 1, the. flare angleinthe vertical plane is greater 1 iselectromagnetic in nature and includes an; electric field componentwhich is parallel tothe.

narrow walls l5 and I6 thereof, and normal to the axis l2. The electricfield vector is,; graphically illustrated at 2|.

is normal to both the electric fieldcomponent 2i and the axis ofpropagation l2.

It will be noted that the horn ID has .anasymmetrical cross section in-a plane taken through theaxis l2 and the m agn etic;field vector :22.The improved performance ofthe horn l0 resultingfrom theasymmetricalconstruction thereof willnqwjbe discussed in connection, with the.diagrammatic representation of an antennasystem illustrated-inFig, 2.As-illustrated the horn-Ill is;attached, at rectangular coupling-sectionH, to, a;corr esponding rectangular wave guide-transmission system 3|suitably supported hyapparatus; not shownin the drawing. The axis 12 isdirected at 7 angle 0 with respect vto the horizontal to acentral pointof aparabolic reflector SZsecuredto an antenna pedestal-33.Theparticular ,system illustrated comprises the basic antennarequirement forasurface or low-, -angle search radar and provides .aradiation pattern having a. principal lobe 34 directed so; that-rnaximum .intensity is obtained in a beam parallel to thesurface oftheearth or .sea. A conventional horn, having an aperturecut in a planenormal to .theaxis of energy transmissionhas side ,lobes due to directradiation-fromthehorn 'in -,a ;plane common to the principalllobe' andthe .liornaxis. .The explanation of this lies. in the substantially in:phase relationship of the aperture illumination ,which maybe.thusconsidered as an effective broadside radiator producing a beamnormal to the long edges. Thus side lobes displaced 90 from the hornaxis are direc fid, atthe horizon. If the principal beam andside lobesof asearch radar are all parallel tothe earth's surfacetargetechoes willproduce multiple and. confusing indications .despite.-th e.

smaller energy content of theside lobes.

Eor t e as mme ca hor structure of, F g. 1 1 sec in a ic te i .2 .thhasep t aper ur l um a io is u orml va iab u t th .q res ond ne un orvar a i n o istanc b w en points alone a ze ss an th displaced 90 fromthe horn axis ,areelevated abovegthe horizon.

=Eig.-3 illustrates thcside lcbes: :3-and fifik fil l r ated asa resultof. currentsin;.th e'.\5v ttica-lly posietioned;edges of .the'hormliishown in Figl 2. The

plane of these side; lobes corresponds :to the .plane,

of the aperture M, the aperture Ibeing shown in Fig. -3 for clarity.These side .lobes i ifiand M are-directed abovethe horizontal :by.an;.angle10,

and are compared with the'horizontalsidelobes 4|- and LIZ whichwouldbeobtained-.ifthe aper-1 ture of the horn were 'cut normal to the "axisThe .magnetic :field. come ponem; may be represented by avector :22which thereof. By thus raising the side lobes of the radiation pattern,the aforementioned spurious, multiple response is eliminated in surfacesearch equipment.

A more general analysis of the radiation pattern of the horn l0indicates that maximum energy is radiated therefrom along the axis l2aspreviously described. Energy is also radiated in.other directionsincluding the sidelobes '43 and 44, and the locus of the vectorindicatin peak energy radiation in a particular direction forms,essentially, a conical surface generated about the vertical axis.IIIIII, illustrated in F 'ig. 2 withvthecenter of the aperture M as the1'5.

vertex. Whenth horn is oriented in the manner illustratedin Fig. 2, peakradiation is horizontal only for theprincipal lobe 34 and all otherradiation is above the horizontal as desired for ,the specific radarapplication described above.

It is evident that the asymmetrical horn structure need not be limited.to the particular pyramidal design illustrated .in Fig. 1. The flareangle and the aperture size will in each instance.

be determined by-the application. of the'radiator structure. Horns ofothercr-oss sectional configuration and other electrical feeds maybeutilized to,provide similar results .if'the'principles described aboveare followed.

Thus, since various modifications andextjen sions of the principleshereinabovese t forth will be evident to those skilled in the art, .Iprefer that thespirit and scope of the present invention-be defined notby thesespecific disclosures but by the appended claims.

Whatis claimed is:

l. Anielectromagnetic horn for interchanging energy between atransmission line .and'space, said horn comprising a,flar,edconductivfeistruce ture terminating in .an aperture at one .end

thereof and a constricted throat'sectionat the opposite end thereof,said aperture and said throat section substantially lying in parallelplanes in non-perpendicular relation with the axis of-said -horn.

v2. A n.electromagnetic radiation system com,- prising a waveguideterminating in an aperture, a flared horn having its'axialextremitieslying inparallel planes, thesmaller of said extremities,being identical to and continuous with the aperture in-said'wave guide,and the parallel-planes determined by said axial extremities beinggi none e cu a w elafion hipw th :the lon iprising, in combination, areflector, a wave guide. 1 and a flared horn integral with'said waveguide illuminating said reflector, the junction of said horn withsaidwaveguideand the 'te'rmination of said horn lying in parallel -planes"-in non-perof said waveguide.

pendicular relationship-with-the longitudinal axis 5. A directionalantenna system for-the-trans mission and reception of; a. beam of energycompris ng, inJcombination ,a reflectoij a wave guide having itslongitudinal axis-angularly displaced from the axis' of l said beam' 1or --energy, aefiarea horn having its smaller end integral with the endof said wave guide, both smaller and larger ends of said flared hornlying in parallel planes in non-perpendicular relationship with thelongitudinal axis of said wave guide.

6. A directional antenna system comprising, a. parabolic reflector forforming a substantially pencil-shaped beam of energy, a rectangularwaveguide, and an electromagnetic horn of conductive material formed byflaring out the walls of said wave guide, the junction of said waveguide and one extremity of said horn comprising a rectangular aperture,the opposite extremity of said horn comprising a larger rectangularaperture lying in a plane parallel to the plane of said first-mentionedrectangular aperture, said and third parallel planes, said transmissionline being joined to said electromagnetic horn in said second plane,said second and third planes being nonperpendicularly related to theaxis of propagation of energy in said electromagnetic horn. said axis ofpropagation of energy being a continuation of the axis of saidtransmission line and being. at an acute angle to saitf'first plane.

LANJEN CHU.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,283,935 King May 26, 19422,362,561 Katzin Nov. 14, 1944 2,364,371 Katzin Dec. 5, 1944 2,369,808Southworth Feb. 20, 1945 2,407,068 Fiske et al. Sept. 3, 1946 2,423,073Willoughby June 24, 1947 2,436,408 Tawney Feb. 24, 1948 FOREIGN PATENTSNumber Country Date 495,977 Great Britain Nov. 23, 1938

